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temperature at the active heating setpoint, while the air valve remains at Airflow Setpoint Reset
Maximum Local Heat.
Figure 12. Single duct VAV unit with modulating hot water or SCR electric heat
Reheat de-energizes when the space temperature rises more than 0.5°F (0.28°C) above the heating
setpoint. When reheat is de-energized, the cooling Airflow Minimum Setpoint is enforced.
The Trane VAV unit's SCR electric heater module takes a 0-to-10 Vdc control signal from AO2. Any
signal less than 0.2 Vdc, and the heater is turned off. For a signal between 0.2 and 10 Vdc, the heater
is on and modulated up to 100% capacity.
Important:
Table 11. Local heat only with no fan present
Configuration
Local
Remote
PWM electric
Not applicable
(1 to 3 stages)
SCR electric
Not applicable
BAS-SVX084A-EN
Discharge air temperatures should not exceed between 100°F and 110°F, with a
temperature between 85°F and 95°F being optimal for space temperature control. If
air that is too hot is delivered to the space through ceiling-mounted diffusers, and
then leaves the space through ceiling-mounted return-air grilles, the buoyancy of
this hot air will tend to cause some of the air to bypass from the supply-air diffusers
to the return-air grilles, resulting in uneven air distribution and possible comfort
complaints. Refer to
Stage 1
• Local PI capacity loop
• Each stage represents an equal percentage of total capacity PWM Output (one stage = 100%; two stages =
50% each; three stages = 33.33% each)
• Total capacity is limited by communicated supply heat control
• Local PI capacity loop
• SCR heat capacity = total capacity
• Total capacity limited by
communicated supply heat control
Calibration, Operation Modes, and Control
Table 11
and
Table 12, p. 46
Method of Control
Stage2
Not applicable
for fan powered reheat.
Stage 3
Not applicable
45
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Troubleshooting
